Apparatus for reducing pellicle darkening

ABSTRACT

Pellicles separated by a distance sufficient to allow a purge gas help repair damage to at least one of the pellicles caused by exposure to an incident radiation and allowing at least a minimum amount of radiation to reach a semiconductor wafer sufficient to perform a desired photolythography process. Moreover, the two pellicles separated by a sufficient distance such that a dispersed purge gas dispersed between the pellicles will not absorb more than an amount of energy from the incident radiation so as to prevent a desired amount of the radiation to reach a semiconductor wafer located a certain distance away from the pellicles.

[0001] Embodiments of the invention relate to semiconductor processing.More specifically, embodiments of the invention relate to extending thelife of pellicles used in conjunction with incident light duringphotolithography without significantly degrading the energy of theincident light.

BACKGROUND

[0002] As photolithography in modern semiconductor processing requireshigher frequency (shorter wavelength) light in order to create smallerdevice dimensions within semiconductor devices, harmful effects to thephotolithography equipment involved in the processing may result. Onesuch harmful effect occurs when fluoropolymer pellicles are exposed tothe high-frequency (high energy) light. Specifically, fluoropolymerpellicles are vulnerable to photochemical darkening when exposed tohigh-frequency light, which can result in the pellicles having to bereplaced more frequently.

[0003] One reason for the premature darkening of fluoropolymer pelliclesis the destruction of chemical bonds within the fluoropolymer pelliclesresulting from the energy transferred from the incident high-frequencylight to the pellicles. The darkening caused by the breaking of chemicalbonds within the pellicles by the incident high-frequency light reducesthe transmission of the light to the underlying semiconductor structureto be exposed to the light.

[0004]FIG. 1 illustrates a prior art photolithography system in which areticle package containing a fluoropolymer pellicle is exposed tohigh-frequency light transmitted through the mask, then projected untothe wafer. Existing reticle packages typically attempt to reduce theeffects of the high-frequency light on the pellicle by producingpellicles that are more transparent and therefore less likely to reactwith the incident light. Because it is difficult to produce a pelliclethat is truly transparent, some photons from the incident light arestill absorbed, resulting in a degradation of the pellicle'stransparency and lifespan.

[0005]FIG. 1 further illustrates the use of N₂ purging in order todispel photon-absorbing compounds, such as O₂ and H₂ 0 found in theatmosphere surrounding the pellicle.

[0006] Exposure of pellicles to a combination of O₂ and N₂ has beenshown to decrease the destructive effects of high-frequency incidentradiation without substantially attenuating the intensity of theradiation when used in proper amounts. Furthermore, other purge gasmixtures, such as H₂/N₂, F₂/N₂, and F₂/H₂/N₂, as well as fluorocarbongases, such as CF₄, and C₂F₆, or a mixture of O₂ with these gases can beused as a suitable purge gas to help extend the transparency life ofpellicles. Other fluorocarbon (FC) gases or hydrofluorocarbon (HFC)gases may also be used as purging gases.

[0007] Excessive amounts of these purge gases, however, can attenuatethe intensity of an incident radiation, thereby altering the intendedeffect upon device features of the semiconductor. For example, exposingan entire reticle to these purge gases could decrease the destructiveeffects by the incident radiation to the pellicle of FIG. 1, but wouldattenuate the incident radiation intensity such that the light would notproperly react with the exposed silicon features on the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments and the invention are illustrated by way of exampleand not limitation in the figures of the accompanying drawings, in whichlike references indicate similar elements and in which:

[0009]FIG. 1 is a prior art stepper system employing a reticle with onepellicle.

[0010]FIG. 2 is a reticle according to one embodiment of the inventionthat employs two pellicles separated by a gap through which a purge gasmay flow.

[0011]FIG. 3 is a flow diagram illustrating the use of at least oneembodiment of the invention.

DETAILED DESCRIPTION

[0012] Embodiments of the invention described herein pertain to astructure and technique for performing photolithography on asemiconductor wafer using high-frequency radiation while substantiallypreserving the optical quality of the pellicle through which theradiation passes. More particularly, embodiments of the inventioninvolve quenching a pellicle or pellicles in a purge gas in order tohelp prevent darkening of the pellicle, thereby extending the lifetimeof the pellicle(s).

[0013]FIG. 2 illustrates a reticle according to one embodiment of theinvention that uses two pellicles 201 separated by a gap 205 throughwhich a purge gas 210 may be dispersed. In the embodiment of theinvention illustrated in FIG. 2, a reticle package contains twopellicles by a relatively small gap in order to allow the a purge gas tobe introduced into the space between the pellicles and the purge gasinlet 203 and outlet 202, without allowing too much gas so as to overlyattenuate the energy of the incident radiation.

[0014] In FIG. 2, incident radiation (light) is applied through theilluminator optics 220, the mask layer 225, through the O₂/N₂ purge gas,and then through the pellicle. The portion of the incident light that isnot blocked by the mask layer 227 passes through the projection optics230 where it is projected onto the particular features on the wafer tobe exposed to the light.

[0015] In the embodiment of the invention illustrated in FIG. 2, thepurge gas is a combination of O₂ and N₂. Other gases, however, may beused, including various combinations of H₂/N₂, F₂/N₂, F₂, H₂, and N₂, aswell as fluorocarbon or hydroflourocarbon gases, such as CF₄ and C₂F₆,or a mixture of O₂ with these gases can be used as a suitable purge gasto help extend the transparency life of pellicles.

[0016] The radiation used in FIG. 2 is 157 nm in wavelength. Embodimentsof the invention, however, may be used in conjunction with radiation ofother wavelengths, including 193 nm and 248 nm. Furthermore, otherphotolithography technologies can be supported in embodiments of theinvention, including I-line and immersion lithography.

[0017] The pellicles of FIG. 2 are separated by approximately 1 mm. Thepellicles, however, may be separated by any distance that is consistentwith the amount of energy from the incident radiation necessary to betransmitted to the wafer and the light-absorbing properties of the purgegas used.

[0018] For example, the pellicles of FIG. 2 are separated by a distance(˜1 mm) such that the O₂ does not absorb more energy from the light thanis desired. Because O₂ strongly absorbs energy from the incident lightstrongly, the distance between the pellicles should be relatively small,so as to provide the desired energy to the wafer. However, if otherpurge gases are used that absorb light less strongly than O₂, thedistance between the pellicles may be greater in order to accommodatemore of the purge gas between the pellicles. The distance between thepellicles, therefore, depends at least in part on the frequency (andtherefore the energy) of the light used as well as the energy absorbencyof the purge gas.

[0019]FIG. 3 is a flow diagram illustrating a use of one embodiment ofthe invention. A stepper positions a reticle containing at least oneembodiment of the invention over a semiconductor wafer in order toexpose the wafer to an incident radiation at operation 301. The wafer isthen exposed to the radiation, which passes through an illuminatoroptic, and a mask at operation 305, then a reticle containing at leastone embodiment of the invention at operation 307. The radiation notblocked by the mask is then introduced to a projection optic whichprojects the radiation onto the wafer at a desired location at operation310.

[0020] While the invention has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments, which are apparent to personsskilled in the art to which the invention pertains are deemed to liewithin the spirit and scope of the invention.

What is claimed is:
 1. An apparatus comprising: a first pellicle; asecond pellicle separated from the first pellicle by a first distance,the first distance being adequate to allow an incident light having afirst energy to pass through a purge gas between the first and secondpellicles while maintaining at least a minimum amount of energy.
 2. Theapparatus of claim 1 wherein the first and second pellicles are within aphotolithography reticle.
 3. The apparatus of claim 1 wherein the purgegas is chosen from a group consisting of N₂/O₂, H₂/N₂, F₂/N₂, F₂,H₂,/N₂, CF₄, and C₂F₆.
 4. The apparatus of claim 3 wherein the purge gascomprises a combination of O₂ and any member of the group of claim
 3. 5.The apparatus of claim 1 wherein the first distance is approximately 1mm.
 6. The apparatus of claim 1 wherein the first energy corresponds tolight having a 157 mm wavelength.
 7. The apparatus of claim 1 whereinthe minimum amount of energy corresponds to an amount of energy desiredto reach a semiconductor wafer positioned a second distance from one ofthe first and second pellicles.
 8. The apparatus of claim 1 wherein thepurge gas is to repair damaged areas of at least one of the first andsecond pellicles resulting from being exposed to the incident light. 9.An apparatus comprising: a first pellicle; a second pellicle parallel tothe first pellicle; a purge gas dispersed between the first and secondpellicles to repair damaged areas of at least one of the first andsecond pellicles resulting from being exposed to an incident light. 10.The apparatus of claim 9 wherein the first and second pellicles arepositioned at opposite sides of a space through which the incidentradiation may pass.
 11. The apparatus of claim 9 wherein the purge gasreduces a rate at which at least one of the first and second pelliclesis darkened by exposure to the incident radiation.
 12. The apparatus ofclaim 9 wherein the purge gas has an energy absorbency sufficient toallow a desired amount of energy of the incident radiation to reach asemiconductor wafer located a first distance from one of the first andsecond pellicles.
 13. The apparatus of claim 9 further comprising anilluminator optic through which the incident radiation may pass beforepassing through the first and second pellicles.
 14. The apparatus ofclaim 13 further comprising a mask through which the incident radiationmay pass before passing through the first and second pellicles.
 15. Theapparatus of claim 14 further comprising a projection optic to project aportion of the incident radiation not blocked by the mask onto asemiconductor wafer.
 16. The apparatus of claim 9 wherein the purge gasis chosen from a group consisting of N₂/O₂, H₂/N₂, F₂/N₂, F₂, H₂,/N₂,CF₄, and C₂F₆.
 17. The apparatus of claim 10 wherein the first andsecond pellicles are separated by approximately 1 mm.
 18. An apparatuscomprising: first means for protecting a semiconductor mask fromcontaminates and for allowing a second portion of incident radiation toreach the semiconductor mask; second means for helping to repair damageto the first means caused by a first portion of the incident radiation.19. The apparatus of claim 18 wherein the first means comprises aplurality of pellicles between which the second means is dispersed. 20.The apparatus of claim 19 wherein at least two of the plurality ofpellicles are separated by a distance sufficient to contain a firstamount of the second means.
 21. The apparatus of claim 20 wherein thesecond means is a purge gas chosen from a group consisting of N2/O2,H₂/N₂, F₂/N₂, F₂, H₂,/N₂, CF₄, and C₂F₆.
 22. The apparatus of claim 21wherein the purge gas comprises a combination of O₂ and any member ofthe group of claim
 21. 23. The apparatus of claim 22 wherein thedistance is inversely proportional to the second portion of the incidentradiation.
 24. The apparatus of claim 23 wherein the first amount of thepurge gas is proportional to the distance.
 25. The apparatus of claim 18wherein the first amount of the purge gas is sufficient to ensure thatthe first portion of the incident radiation is substantially equal tothe second portion of the incident radiation.
 26. A system comprising: asemiconductor wafer; a reticle to expose the semiconductor wafer to anincident radiation having a wavelength of approximately 157 nm, thereticle including two pellicles separated by a first distance and by apurge gas through which the incident light may pass without losing asufficient amount of energy to be delivered to the semiconductor wafer.27. The system of claim 26 wherein the purge gas is to help repairdamaged areas of at least one of the two pellicles resulting from beingexposed to the incident light.
 28. The system of claim 26 wherein thedistance by which the two pellicles are separated depends upon an amountof purge gas to be dispersed between the two pellicles.
 29. The systemof claim 28 wherein a space defined on two opposite sides by the twopellicles is further defined on two opposite sides adjacent to the twopellicles by a purge gas inlet and a purge gas outlet through which thepurge gas may pass.
 30. The system of claim 29 wherein the distance bywhich the two pellicles are separated is approximately 1 mm.
 31. Amethod comprising: positioning a reticle above a semiconductor wafer;exposing the semiconductor wafer to an incident radiation, which passesthrough two pellicles separated by a distance within which a purge gascomprising O₂ is dispersed.
 32. The method of claim 31 wherein the purgegas further comprises a gas chosen from a group consisting of N₂, H₂/N₂,F₂/N₂, F₂, H₂,/N₂, CF₄, and C₂F₆.
 33. The method of claim 31 wherein theincident radiation has a wavelength chosen from a group consisting ofapproximately 157 nm, approximately 193 nm, and approximately 248 nm.34. The method of claim 31 comprising a photolithography process.